Earth-boring tools for forming wellbores in subterranean earth formations may include a plurality of cutting elements secured to a body. For example, fixed-cutter earth-boring rotary drill bits (also referred to as “drag bits”) include a plurality of cutting elements that are fixedly attached to a bit body of the drill bit, conventionally in pockets formed in blades and other exterior portions of the bit body. Rolling cone earth-boring drill bits include a plurality of cutters attached to bearing pins on legs depending from a bit body. The cutters may include cutting elements (sometimes called “teeth”) milled or otherwise formed on the cutters, which may include hardfacing on the outer surfaces of the cutting elements, or the cutters may include cutting elements (sometimes called “inserts”) attached to the cutters, conventionally in pockets formed in the cutters. Other bits might include impregnated bits that typically comprise a body having a face comprising a superabrasive impregnated material, conventionally a natural or synthetic diamond grit or thermally stable diamond elements dispersed in a matrix of surrounding body material or segments of matrix material brazed to the bit body.
The cutting elements used in such earth-boring tools often include polycrystalline diamond cutters (PDCs), which are cutting elements that include a polycrystalline diamond (PCD) material. Such polycrystalline diamond cutting elements are formed by sintering and bonding together relatively small diamond grains or crystals under conditions of high temperature and high pressure in the presence of a catalyst (such as, for example, cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high temperature/high pressure (or HTHP) processes. The cutting element substrate may comprise a cermet material (i.e., a ceramic-metal composite material) comprising a plurality of particles of hard material in a metal matrix, such as, for example, cobalt-cemented tungsten carbide. In such instances, catalyst material in the cutting element substrate may be drawn into the diamond grains or crystals during sintering and catalyze formation of a diamond table from the diamond grains or crystals. In other methods, powdered catalyst material may be mixed with the diamond grains or crystals prior to sintering the grains or crystals together in an HTHP process.
Exposed portions of cutting elements, such as, for example, diamond tables, portions of substrates, hardfacing disposed on the outer surfaces of cutting elements, and exposed surfaces of the earth-boring tool, such as, for example, blade surfaces, fluid course surfaces, and junk slot surfaces of a fixed-cutter drill bit or the cutters of a rolling cone drill bit, may be subject to failure modes, such as, for example, erosion, fracture, spalling, and diamond table delamination, due to abrasive wear, impact forces, and vibration during drilling operations from contact with the formation being drilled. Some portions of the earth-boring tool may be more susceptible to such failure modes, and localized wear and localized impact damage may cause the earth-boring tool to fail prematurely while leaving other portions of the earth-boring tool in a usable condition. For example, cutting elements and the blades to which they are attached may be more susceptible to failure at the shoulder region of a face of the bit body as compared to the cone and nose regions of the face of the bit body or the gage region of the bit body. In instances of cutting element failure or blade structure failure leading to cutting elements loss at a particular radial location from the bit centerline, an annular groove may wear into the face of the bit body at the shoulder region, a phenomenon sometimes referred to as “ring out.” Further, cutting elements and the blades to which they are attached may be susceptible to failure within a central, core region of a drill bit located within the cone or nose regions of the face thereof, resulting in “core out.” Other earth-boring tools may similarly exhibit localized wear in certain portions of the earth-boring tools.
To address such concerns, so-called “self-sharpening” tools have been proposed, for example, in U.S. Application Publication No. 2010/0089649 A1 published Apr. 15, 2010 to Welch et al., the disclosure of which is hereby incorporated herein in its entirety by this reference. Briefly, portions of an earth-boring tool, such as, for example, portions of the blades of a fixed-cutter bit, may wear away during drilling and expose embedded or partially embedded cutting elements at the same radial locations to begin engaging the formation as cutting elements that were originally exposed at those radial locations to engage the formation fail and become detached from the earth-boring tool. Due to the complexity and difficulty of positioning and embedding or partially embedding the cutting elements within the earth-boring tools, however, such self-sharpening tools have been difficult and costly to manufacture.